Implant for an ostheosynthesis device, in particular for the spine

ABSTRACT

An implant for an ostheosynthesis device, in particular for the spine, comprises an anchoring portion (11) for anchoring to bone and a body in which a channel (13) is formed suitable for receiving a rod (T), the channel opening out sideways in the body, a hollow element (20) suitable for surrounding the body (12) and possessing two notches suitable for receiving the rod on either side of the body (12), and a screw (30) for fixing the hollow element on the body. According to the invention: the hollow element is a cover (20) fitting over the body with a rounded top portion (21b) in which an opening (25) is formed, the body (12) includes a tapped hole (14) facing said opening, and the head (31) of a screw (30) bears against the top (21b, 25a) of the cover, its threaded portion (32) being screwed in the tapped hole through said opening.

The present invention relates to the field of implants forostheosynthesis, in particular for the spine, and more particularly itrelates to an implant for an ostheosynthesis device, in particular forthe spine, of the type comprising an anchoring portion for anchoring tobone and a body in which a channel is formed suitable for receiving arod, the channel opening out sideways in the body, a hollow elementsuitable for surrounding the body and possessing two notches suitablefor receiving the rod on either side of the body, and means for fixingthe hollow element on the body.

Document EP-A-0 517 059 teaches an implant of that type.

Nevertheless, that known implant suffers from a certain number ofdrawbacks. Firstly, it is relatively bulky because the body of theimplant possesses a threaded extension extending backwardly, with thefixing means consisting in a nut of relatively large dimensions screwedonto the extension. In addition, by its very nature, the nut hasprojecting angles which are generally undesirable for implants sincethey damage the environment.

Also, nut tightening generally needs to be performed with an extremelylarge amount of torque, and as a result during tightening there is arisk of metal particles being torn off and released from the threads ofthe nut and/or the threaded extension, thus running the risk ofmetallosis developing in the patient.

The present invention seeks to mitigate or at least to attenuate allthose drawbacks of the prior art.

To this end, it proposes an implant of the type mentioned in theintroduction and characterized in that:

the hollow element is constituted by a cover fitting over the body andhaving a rounded top portion in which an opening is formed;

the body including a tapped hole facing said opening; and

the fixing means comprising a screw having a head that bears against thetop portion of the cover and a threaded portion that is screwed in thetapped hole.

Advantageously, going from the outside towards the center of the body,the channel slopes towards the bone anchoring portion.

In a preferred embodiment, the body has a top portion that issubstantially hemispherical in shape and the cover has a top portionthat is of complementary substantially hemispherical shape; thenpreferably, the head of the screw has an outside surface that extendsthe rounded top surface of the cover with continuity.

In the same spirit, the invention also provides an implant for anostheosynthesis device, in particular for the spine, of the typecomprising an anchoring portion for anchoring to bone and a body inwhich a channel is formed suitable for receiving a rod, the channelopening out sideways in the body, a hollow element fixed on the body tohold the rod in the channel, and means for fixing the hollow element onthe body, the implant being characterized in that:

going from the outside towards the center of the body, the channelslopes towards the bone anchoring portion; and

the hollow element fits over the body and possesses a rounded topportion terminated by a generally flat edge bearing against the rod ateither end of the channel to lock said rod in the channel, an openingbeing formed in said top portion;

the body including a tapped hole facing said opening; and

the fixing means comprising a screw having a head that bears against thetop portion of the hollow element and a threaded portion that is screwedin the tapped hole.

Advantageously, the body has a top portion that is substantiallyhemispherical in shape and the hollow element comprises a cap that is ofcomplementary substantially hemispherical shape.

Then preferably, the head of the screw has an outside surface thatextends the rounded top surface of the cap with continuity.

Finally, it is appropriate for the screw to be mounted in unloseablemanner in the opening of the hollow element.

Other aspects, objects, and advantages of the present invention appearmore clearly on reading the following detailed description of preferredembodiments thereof given by way of example and made with reference tothe accompanying drawing, in which:

FIG. 1 is an exploded perspective view of an implant of the inventionand an associated rod;

FIG. 2 is a perspective view of the implant and the rod in the assembledstate;

FIG. 3 is an elevation view from the side of a portion of the implant;and

FIG. 4 is an elevation view from the side of an implant constituting avariant embodiment of the invention.

With reference to the drawing, there can be seen an implant forostheosynthesis of the spine which comprises a first element 10 foranchoring to bone and a body 12 for fixing the element 10 to a rod T.

The anchoring portion 11 is implemented in this case in the form of acurved pedicle hook with the edge of its free end possessing a notch 11ain conventional manner.

The body 12 formed integrally with the hook 11 has a generallycylindrically shaped outline in a base region 12a extending from thehook 11. Remote from the hook it is terminated by a top region 12b whichis generally hemispherical in shape.

A channel 13 is formed in the base portion 12a of the body 12 to receivethe rod T. The channel opens out generally sideways and its height isslightly greater than the diameter of the rod T.

As can be seen in particular in FIG. 3, the channel 13 has a slightdownwards slope going from the outside towards the center of the body12, and it is defined by a top wall 13a and a bottom wall 13b that areparallel to each other and that provide the above-mentioned slope, andalso by an end wall 13c that is generally semi-cylindrical.

The channel extends across the entire width of the body 12 and the rod Tcan be inserted sideways therein until it reaches the end, the end andthe rod being complementary in shape.

The body 12 also possesses a tapped hole 14 which extends downwardsalong the axis of the body from the top region 12b of its hemisphericalfree end.

In the present example, the tapped hole passes through the top wall 13aof the channel 13, however in a variant it could be a blind hole openonly to the top of the body 12.

The implant of the invention also comprises a cover or cap 20 suitablefor fitting over the body 12 having the rod T installed in its channel15. The cover has a wall 21 with a base region 21a which is generallycircularly cylindrical and a top region 21b which is generallyhemispherical in shape. The cover 20 defines an inside cavity 22 whoseshape, at least in cross-section, is identical to the outside shape ofthe body 12, so as to be capable of fitting thereover with as littletransverse play as possible, while nevertheless not impeding easysliding between the body 12 and the cover 20 while the cover is beingput into place.

Wall portion 21a has two generally U-shaped notches 23 in twodiametrically opposite regions, only one notch being visible in FIGS. 1and 2, which notches extend parallel to the axis of the cover(vertically in the figures). Each notch extends upwards from the bottomedge of the wall 21a over a length that is slightly longer than thediameter of the rod T and terminates at a well-defined height in asemicircular end so as to be complementary in shape to the top of therod.

The top of the cover 20 has an opening 25 of diameter equal to orslightly greater than the diameter of the tapped hole 14 in the body 12.This opening has a peripheral chamfer referenced 25a.

Finally, the implant of the invention comprises a screw 30 having a head31 and a threaded portion 32 complementary to the tapping formed in thebody 12.

The bottom surface of the head 31 around the portion 32 is chamfered tomatch the chamfer 25a of the cover.

The shape of the top surface of the head 31 is that of a portion of asphere having approximately the same radius as the outer sphericalsurface of the top portion 21b of the cover. Thus, when in place, thehead 31 can be flush with the outside surface of the top portion 21b ofthe cover.

Also, it is advantageous for the thread of the screw 30 and the diameterof the opening 25 to be designed in such a manner as to ensure that thescrew 30 can be held loose in said opening prior to assembly, so as tomake the screw unloseable. This is advantageously achieved by giving theopening 25 a diameter that is slightly smaller than the overall outsidediameter of the threads of the screw.

For the surgeon, this greatly simplifies the handling of the variousportions of the implant.

In this top surface, there is formed a handling and tightening facility,in this case a six-sided hexagonal socket 33 for receiving the end of an"Allen" type key.

The various elements of the implant as described above are naturallymade out of a material that is biocompatible, such as a titanium alloyor stainless steel.

The implant as described above is put into place as follows: firstly theanchoring portion 11 is placed on a vertebra in the usual manner so asto position the body 12 in the desired location. The rod T is thenengaged sideways into the channel 13 until it engages the end thereof.It is important to observe at this point that the hemispherical shape ofthe top 12b of the body 12, and the slope of the channel 13 as indicatedabove serve to make this engagement easier to perform, particularly whenthe rod T has already been secured to one or more other implants. If therod T is brought to the vicinity of the top of the implant and if it isthen pushed down towards the side having the entrance to the channel 13,then the rod will slide progressively and without encountering anyobstacle over the side of the body 12 and will then penetrate easilyinto the channel 13 as soon as it overlies it.

Thereafter, the cover 20 is put into place over the body 12 of theelement 10 and over the rod T, with the rod being received in the twonotches 23 at each of the diametrically opposite outlet ends of thechannel, the notches being appropriately prepositioned for this purpose.

It will be observed that from this instant, the cover 20 is preventedfrom rotating by the rod T co-operating with the notches 23.

The screw is then engaged in the opening 25 and tightened in the tapping14 by means of an appropriate tool, thereby securing the cover or cap 20on the body 12 and holding the rod T firmly captive. It may be observedat this point that the end of each notch 23 is positioned so as to bearagainst the rod T before the end of the cavity 22 in the cover 20 comesto bear against the dome 12b of the body 12, so as to ensure that therod is effectively locked.

After being assembled and locked, the implant is as shown in FIG. 2. Itcan be seen that there is practically no outwardly directed projectingangle. In particular, the head of the screw 30 extends the dome-shapesurface of the cover in continuous manner. It can also be seen that therisks of particles of matter becoming dislodged during tightening of thescrew at high torque exist almost solely in regions inside the implant,i.e. inside the tapped hole 14, thereby reducing the risks ofmetallosis.

FIG. 4 shows a variant embodiment of the invention. In this variant, thecover 20 comprises no more than a generally hemispherical wall that iscomplementary to the hemispherical region 12b of the body, and towardsthe anchoring portion 11 it is terminated in an annular flat edge 26.

When the cover 20 is secured to the body 12 by means of the screw 30, asdescribed above, the edge 26 comes to bear on the rod T on either sideof the channel 13 so as to lock said rod. In this variant, it isnecessary for the channel to tilt substantially, as shown, in order toachieve satisfactory locking since the cover 20 no longer has thenotches 23 of FIGS. 1 and 3 and it is only its edge 26 that opposesmovement of the rod T out from the channel 13: the greater theinclination of the edge 26 relative to the escape direction of the rodfrom the channel, the more effective the opposition.

Naturally, the present invention is not limited to the embodimentsdescribed above and shown in the drawings, and the person skilled in theart will be able to apply any variants or modifications within thespirit of the invention.

In particular, although the bone anchoring portion 11 is described asbeing a hook, it could also be a screw such as a pedicle screw, interalia.

We claim:
 1. An implant for an osteosynthesis device, comprising:ananchoring portion for anchoring to bone; a body having a channel openingsideways in said body for receiving a rod and having a tapped hole, saidchannel sloping toward said anchoring portion from an outside portionthereof towards a center of said body; a hollow cover fitting over andsurrounding said body, said cover having a dome-shaped top portion witha opening extending therethrough and having two notches for receivingthe rod on either side of said body, said opening facing said tappedhole; and a screw having a head bearing against said top portion of saidcover and a threaded portion extending through said opening andthreadedly engaged in said tapped hole in said body to affix said coveron said body.
 2. An implant according to claim 1 whereinsaid bodycomprises a top portion which is hemispherical in shape; and saiddome-shaped top portion of said cover has a hemispherical shapecomplimentary to said top portion of said body.
 3. An implant accordingto claim 2 whereinsaid head of said screw comprises an outside surfacewith a curvature forming a continuation of said dome-shaped top portionof said cover.
 4. An implant according to claim 1 whereinsaid head ofsaid screw comprises an outside surface with a curvature forming acontinuation of said dome-shaped top portion of said cover.
 5. Animplant according to claim 4 whereinsaid head of said screw comprises asocket for receiving and forming a torque transmitting connection with atool.
 6. An implant according to claim 1 whereinsaid head of said screwcloses said opening in said cover.
 7. An implant according to claim 1whereinsaid tapped hole extends along a longitudinal axis of said body;and said channel extends generally transverse to said longitudinal axis.8. An implant for an osteosynthesis device, comprising:an anchoringportion for anchoring to bone; a body having a channel opening sidewaysin said body and having a tapped hole, said channel sloping toward saidanchoring portion from an outside portion thereof towards a center ofsaid body; a rod received in said channel; a hollow cover fitting oversaid body and having a dome-shaped top portion terminating in agenerally flat annular edge bearing against said rod adjacentlongitudinal ends of said channel to lock said rod in said channel; anopening in said top portion of said cover; a tapped hole in said bodyfacing said opening; and a screw having a head bearing against said topportion of said cover and having a threaded portion extending throughsaid opening and threaded in said tapped hole to fix said cover on saidbody.
 9. An implant according to claim 8 whereinsaid body comprises atop portion which is hemispherical in shape; and said cover comprises acap having a hemispherical shape complementary to said top portion ofsaid body.
 10. An implant according to claim 9 whereinsaid head of saidscrew comprises an outside surface with a curvature forming acontinuation of said hemispherical shape of said cap.
 11. An implantaccording to claim 8 whereinsaid screw is fixed in said opening in saidcover.
 12. An implant according to claim 11 whereinsaid head of saidscrew comprises an outside surface with a curvature forming acontinuation of said hemispherical shape of said cap.
 13. An implantaccording to claim 8 whereinsaid head of said screw comprises an outsidesurface with a curvature forming a continuation of said hemisphericalshape of said cap.
 14. An implant according to claim 13 whereinsaid headof said screw comprises a socket for receiving and forming a torquetransmitting connection with a tool.
 15. An implant according to claim 8whereinsaid head of said screw closes said opening in said cover.
 16. Animplant according to claim 8 whereinsaid tapped hole extends along alongitudinal axis of said body; and said channel extends generallytransverse to said longitudinal axis.